DER : Java Glossary

DER (Distinguished Encoding Rules)
A more rigid way than BER (Basic Encoding Rules) for encoding binary
interchange records described by ASN.1 (Abstract Syntax Notation 1).
The idea is there must be one and only one possible way to encode any data so that
if two people encode it, guaranteed they will do it exactly the same way. You need
this feature in digital certificates when computing digests.